Language/OS - Multiplatform Resource Library/LANGUAGE OS.iso/pcl/pcl-rev4.lha/cache.lisp

Lisp/Scheme | 1990-10-10 | 39KB | 1,081 lines

;;;-*-Mode:LISP; Package:(PCL LISP 1000); Base:10; Syntax:Common-lisp -*-
;;;
;;; *************************************************************************
;;; Copyright (c) 1985, 1986, 1987, 1988, 1989, 1990 Xerox Corporation.
;;; All rights reserved.
;;;
;;; Use and copying of this software and preparation of derivative works
;;; based upon this software are permitted.  Any distribution of this
;;; software or derivative works must comply with all applicable United
;;; States export control laws.
;;;
;;; This software is made available AS IS, and Xerox Corporation makes no
;;; warranty about the software, its performance or its conformity to any
;;; specification.
;;;
;;; Any person obtaining a copy of this software is requested to send their
;;; name and post office or electronic mail address to:
;;;   CommonLoops Coordinator
;;;   Xerox PARC
;;;   3333 Coyote Hill Rd.
;;;   Palo Alto, CA 94304
;;; (or send Arpanet mail to [e-mail])
;;;
;;; Suggestions, comments and requests for improvements are also welcome.
;;; *************************************************************************
;;;
;;; The basics of the PCL wrapper cache mechanism.
;;;

(in-package 'pcl)
;;;
;;; The caching algorithm implemented:
;;;
;;; << put a paper here >>
;;;
;;; For now, understand that as far as most of this code goes, a cache has
;;; two important properties.  The first is the number of wrappers used as
;;; keys in each cache line.  Throughout this code, this value is always
;;; called NKEYS.  The second is whether or not the cache lines of a cache
;;; store a value.  Throughout this code, this always called VALUEP.
;;;
;;; Depending on these values, there are three kinds of caches.
;;;
;;; NKEYS = 1, VALUEP = NIL
;;;
;;; In this kind of cache, each line is 1 word long.  No cache locking is
;;; needed since all read's in the cache are a single value.  Nevertheless
;;; line 0 (location 0) is reserved, to ensure that invalid wrappers will
;;; not get a first probe hit.
;;;
;;; To keep the code simpler, a cache lock count does appear in location 0
;;; of these caches, that count is incremented whenever data is written to
;;; the cache.  But, the actual lookup code (see make-dlap) doesn't need to
;;; do locking when reading the cache.
;;;
;;;
;;; NKEYS = 1, VALUEP = T
;;;
;;; In this kind of cache, each line is 2 words long.  Cache locking must
;;; be done to ensure the synchronization of cache reads.  Line 0 of the
;;; cache (location 0) is reserved for the cache lock count.  Location 1
;;; of the cache is unused (in effect wasted).
;;;
;;; NKEYS > 1
;;;
;;; In this kind of cache, the 0 word of the cache holds the lock count.
;;; The 1 word of the cache is line 0.  Line 0 of these caches is not
;;; reserved.
;;;
;;; This is done because in this sort of cache, the overhead of doing the
;;; cache probe is high enough that the 1+ required to offset the location
;;; is not a significant cost.  In addition, because of the larger line
;;; sizes, the space that would be wasted by reserving line 0 to hold the
;;; lock count is more significant.
;;;


;;;
;;; Caches
;;;
;;; A cache is essentially just a vector.  The use of the individual `words'
;;; in the vector depends on particular properties of the cache as described
;;; above.
;;;
;;; This defines an abstraction for caches in terms of their most obvious
;;; implementation as simple vectors.  But, please notice that part of the
;;; implementation of this abstraction, is the function lap-out-cache-ref.
;;; This means that most port-specific modifications to the implementation
;;; of caches will require corresponding port-specific modifications to the
;;; lap code assembler.
;;;
(defmacro cache-ref (cache location)
  `(svref (the simple-vector ,cache) (the fixnum ,location)))

(defun emit-cache-ref (cache-operand location-operand)
  (operand :iref cache-operand location-operand))


(defun cache-size (cache)
  (array-dimension (the simple-vector cache) 0))

(defun allocate-cache (size)
  (make-array size :adjustable nil))

(defmacro cache-lock-count (cache)
  `(cache-ref ,cache 0))

(defun flush-cache-internal (cache)
  (without-interrupts
    (fill (the simple-vector cache) nil)
    (setf (cache-lock-count cache) 0))
  cache)

(defmacro modify-cache (cache &body body)
  `(without-interrupts
     (multiple-value-prog1
       (progn ,@body)
       (let ((old-count (cache-lock-count ,cache)))
     (setf (cache-lock-count ,cache)
           (if (= old-count most-positive-fixnum) 1 (1+ old-count)))))))



;;;
;;; Some facilities for allocation and freeing caches as they are needed.
;;; This is done on the assumption that a better port of PCL will arrange
;;; to cons these all the same static area.  Given that, the fact that
;;; PCL tries to reuse them should be a win.
;;;
(defvar *free-caches* (make-hash-table :size 16))

;;;
;;; Return a cache that has had flush-cache-internal called on it.  This
;;; returns a cache of exactly the size requested, it won't ever return a
;;; larger cache.
;;;
(defun get-cache (size)
  (let ((entry (gethash size *free-caches*)))
    (without-interrupts
      (cond ((null entry)
         (setf (gethash size *free-caches*) (cons 0 nil))
         (get-cache size))
        ((null (cdr entry))
         (incf (car entry))
         (flush-cache-internal (allocate-cache size)))
        (t
         (let ((cache (cdr entry)))
           (setf (cdr entry) (cache-ref cache 0))
           (flush-cache-internal cache)))))))

(defun free-cache (cache)
  (let ((entry (gethash (cache-size cache) *free-caches*)))
    (without-interrupts
      (if (null entry)
      (error "Attempt to free a cache not allocated by GET-CACHE.")
      (let ((thread (cdr entry)))
        (loop (unless thread (return))
          (when (eq thread cache) (error "Freeing a cache twice."))
          (setq thread (cache-ref thread 0)))
        (flush-cache-internal cache)        ;Help the GC
        (setf (cache-ref cache 0) (cdr entry))
        (setf (cdr entry) cache)
        nil)))))

;;;
;;; This is just for debugging and analysis.  It shows the state of the free
;;; cache resource.
;;;
(defun show-free-caches ()
  (let ((elements ()))
    (maphash #'(lambda (s e) (push (list s e) elements)) *free-caches*)
    (setq elements (sort elements #'< :key #'car))
    (dolist (e elements)
      (let* ((size (car e))
         (entry (cadr e))
         (allocated (car entry))
         (head (cdr entry))
         (free 0))
    (loop (when (null head) (return t))
          (setq head (cache-ref head 0))
          (incf free))
    (format t
        "~&There  ~4D are caches of size ~4D. (~D free  ~3D%)"
        allocated
        size
        free
        (floor (* 100 (/ free (float allocated)))))))))


;;;
;;; Wrapper cache numbers
;;;

;;;
;;; The constant WRAPPER-CACHE-NUMBER-ADDS-OK controls the number of non-zero
;;; bits wrapper cache numbers will have.
;;;
;;; The value of this constant is the number of wrapper cache numbers which
;;; can be added and still be certain the result will be a fixnum.  This is
;;; used by all the code that computes primary cache locations from multiple
;;; wrappers.
;;;
;;; The value of this constant is used to derive the next two which are the
;;; forms of this constant which it is more convenient for the runtime code
;;; to use.
;;;
(eval-when (compile load eval)

(defconstant wrapper-cache-number-adds-ok 4)

(defconstant wrapper-cache-number-length
         (- (integer-length most-positive-fixnum)
        wrapper-cache-number-adds-ok))

(defconstant wrapper-cache-number-mask
         (1- (expt 2 wrapper-cache-number-length)))


(defvar *get-wrapper-cache-number* (make-random-state))

(defun get-wrapper-cache-number ()
  (let ((n 0))
    (loop
      (setq n
        (logand wrapper-cache-number-mask
            (random most-positive-fixnum *get-wrapper-cache-number*)))
      (unless (zerop n) (return n)))))


(unless (> wrapper-cache-number-length 8)
  (error "In this implementation of Common Lisp, fixnums are so small that~@
          wrapper cache numbers end up being only ~D bits long.  This does~@
          not actually keep PCL from running, but it may degrade cache~@
          performance.~@
          You may want to consider changing the value of the constant~@
          WRAPPER-CACHE-NUMBER-ADDS-OK.")))


;;;
;;; wrappers themselves
;;;
;;; This caching algorithm requires that wrappers have more than one wrapper
;;; cache number.  You should think of these multiple numbers as being in
;;; columns.  That is, for a given cache, the same column of wrapper cache
;;; numbers will be used.
;;;
;;; If at some point the cache distribution of a cache gets bad, the cache
;;; can be rehashed by switching to a different column.
;;;
;;; The columns are referred to by field number which is that number which,
;;; when used as a second argument to wrapper-ref, will return that column
;;; of wrapper cache number.
;;;
;;; This code is written to allow flexibility as to how many wrapper cache
;;; numbers will be in each wrapper, and where they will be located.  It is
;;; also set up to allow port specific modifications to `pack' the wrapper
;;; cache numbers on machines where the addressing modes make that a good
;;; idea.
;;;
(eval-when (compile load eval)
(defconstant wrapper-layout
         '(number
           number
           number
           number
           number
           number
           number
           number
           state
           instance-slots-layout
           class-slots
           class))
)

(eval-when (compile load eval)

(defun wrapper-field (type)
  (position type wrapper-layout))

(defun next-wrapper-field (field-number)
  (position (nth field-number wrapper-layout)
        wrapper-layout
        :start (1+ field-number)))

);eval-when

(defmacro wrapper-ref (wrapper n)
  `(svref ,wrapper ,n))

(defun emit-wrapper-ref (wrapper-operand field-operand)
  (operand :iref wrapper-operand field-operand))


(defmacro wrapper-state (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'state)))

(defmacro wrapper-instance-slots-layout (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'instance-slots-layout)))

(defmacro wrapper-class-slots (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'class-slots)))

(defmacro wrapper-class (wrapper)
  `(wrapper-ref ,wrapper ,(wrapper-field 'class)))


(defmacro make-wrapper-internal ()
  `(let ((wrapper (make-array ,(length wrapper-layout) :adjustable nil)))
     ,@(gathering1 (collecting)
     (iterate ((i (interval :from 0))
           (desc (list-elements wrapper-layout)))
       (ecase desc
         (number
          (gather1 `(setf (wrapper-ref wrapper ,i)
                  (get-wrapper-cache-number))))
         ((state instance-slots-layout class-slots class)))))
     (setf (wrapper-state wrapper) 't)
     wrapper))

(defun make-wrapper (class)
  (let ((wrapper (make-wrapper-internal)))
    (setf (wrapper-class wrapper) class)
    wrapper))

;;;
;;; The wrapper cache machinery provides general mechanism for trapping on
;;; the next access to any instance of a given class.  This mechanism is
;;; used to implement the updating of instances when the class is redefined
;;; (make-instances-obsolete).  The same mechanism is also used to update
;;; generic function caches when there is a change to the supers of a class.
;;;
;;; Basically, a given wrapper can be valid or invalid.  If it is invalid,
;;; it means that any attempt to do a wrapper cache lookup using the wrapper
;;; should trap.  Also, methods on slot-value-using-class check the wrapper
;;; validity as well.  This is done by calling check-wrapper-validity.
;;;

(defun invalid-wrapper-p (wrapper)
  (neq (wrapper-state wrapper) 't))

(defvar *previous-nwrappers* (make-hash-table))

(defun invalidate-wrapper (owrapper state nwrapper)
  (ecase state
    ((flush obsolete)
     (let ((new-previous ()))
       ;;
       ;; First off, a previous call to invalidate-wrapper may have recorded
       ;; owrapper as an nwrapper to update to.  Since owrapper is about to
       ;; be invalid, it no longer makes sense to update to it.
       ;;
       ;; We go back and change the previously invalidated wrappers so that
       ;; they will now update directly to nwrapper.  This corresponds to a
       ;; kind of transitivity of wrapper updates.
       ;;
       (dolist (previous (gethash owrapper *previous-nwrappers*))
     (when (eq state 'obsolete)
       (setf (car previous) 'obsolete))
     (setf (cadr previous) nwrapper)
     (push previous new-previous))

       (iterate ((type (list-elements wrapper-layout))
         (i (interval :from 0)))
     (when (eq type 'number) (setf (wrapper-ref owrapper i) 0)))
       (push (setf (wrapper-state owrapper) (list state nwrapper))
         new-previous)

       (setf (gethash owrapper *previous-nwrappers*) ()
         (gethash nwrapper *previous-nwrappers*) new-previous)))))

(defun check-wrapper-validity (instance)
  (let* ((owrapper (wrapper-of instance))
     (state (wrapper-state owrapper)))
    (if (eq state  't)
    owrapper
    (let ((nwrapper
        (ecase (car state)
          (flush
            (flush-cache-trap owrapper (cadr state) instance))
          (obsolete
            (obsolete-instance-trap owrapper (cadr state) instance)))))
      ;;
      ;; This little bit of error checking is superfluous.  It only
      ;; checks to see whether the person who implemented the trap
      ;; handling screwed up.  Since that person is hacking internal
      ;; PCL code, and is not a user, this should be needless.  Also,
      ;; since this directly slows down instance update and generic
      ;; function cache refilling, feel free to take it out sometime
      ;; soon.
      ;;
      (cond ((neq nwrapper (wrapper-of instance))
         (error "Wrapper returned from trap not wrapper of instance."))
        ((invalid-wrapper-p nwrapper)
         (error "Wrapper returned from trap invalid.")))
      nwrapper))))



(defun compute-line-size (nelements) (expt 2 (ceiling (log nelements 2))))

(defun compute-cache-parameters (nkeys valuep nlines-or-cache)
  (declare (values cache-mask actual-size line-size nlines))
  (flet ((compute-mask (cache-size line-size)
       (logxor (1- cache-size) (1- line-size))))
    (if (= nkeys 1)
    (let* ((line-size (if valuep 2 1))
           (cache-size (if (numberp nlines-or-cache)
                   (* line-size
                  (expt 2 (ceiling (log nlines-or-cache 2))))
                   (cache-size nlines-or-cache))))
      (values (compute-mask cache-size line-size)
          cache-size
          line-size
          (/ cache-size line-size)))
    (let* ((line-size (compute-line-size (+ nkeys (if valuep 1 0))))
           (cache-size (if (numberp nlines-or-cache)
                   (* line-size
                  (expt 2 (ceiling (log nlines-or-cache 2))))
                   (1- (cache-size nlines-or-cache)))))
      (values (compute-mask cache-size line-size)
          (1+ cache-size)
          line-size
          (/ cache-size line-size))))))



;;;
;;; The various implementations of computing a primary cache location from
;;; wrappers.  Because some implementations of this must run fast there are
;;; several implementations of the same algorithm.
;;;
;;; The algorithm is:
;;;
;;;  SUM       over the wrapper cache numbers,
;;;  ENSURING  that the result is a fixnum
;;;  MASK      the result against the mask argument.
;;;
;;;

;;;
;;; COMPUTE-PRIMARY-CACHE-LOCATION
;;;
;;; The basic functional version.  This is used by the cache miss code to
;;; compute the primary location of an entry.
;;;
(defun compute-primary-cache-location (field mask wrappers)
  (if (not (consp wrappers))
      (logand mask (wrapper-ref wrappers field))
      (let ((location 0))
    (iterate ((wrapper (list-elements wrappers))
          (i (interval :from 0)))
      ;;
      ;; First add the cache number of this wrapper to location.
      ;;
      (let ((wrapper-cache-number (wrapper-ref wrapper field)))
        (if (zerop wrapper-cache-number)
        (return-from compute-primary-cache-location 0)
        (setq location (+ location wrapper-cache-number))))
      ;;
      ;; Then, if we are working with lots of wrappers, deal with
      ;; the wrapper-cache-number-mask stuff.
      ;;
      (when (and (not (zerop i))
             (zerop (mod i wrapper-cache-number-adds-ok)))
        (setq location
          (logand location wrapper-cache-number-mask))))
    (1+ (logand mask location)))))

;;;
;;; COMPUTE-PRIMARY-CACHE-LOCATION-FROM-LOCATION
;;;
;;; This version is called on a cache line.  It fetches the wrappers from
;;; the cache line and determines the primary location.  Various parts of
;;; the cache filling code call this to determine whether it is appropriate
;;; to displace a given cache entry.
;;;
;;; If this comes across a wrapper whose cache-no is 0, it returns the symbol
;;; invalid to suggest to its caller that it would be provident to blow away
;;; the cache line in question.
;;;
(defun compute-primary-cache-location-from-location (field cache location mask nkeys)
  (let ((result 0))
    (dotimes (i nkeys)
      (let* ((wrapper (cache-ref cache (+ i location)))
         (wcn (wrapper-ref wrapper field)))
    (setq result (+ result wcn)))
      (when (and (not (zerop i))
         (zerop (mod i wrapper-cache-number-adds-ok)))
    (setq result (logand result wrapper-cache-number-mask)))
      )
    (if (= nkeys 1)
    (logand mask result)
    (1+ (logand mask result)))))

(defun emit-1-wrapper-compute-primary-cache-location (wrapper primary wrapper-cache-no)
  (with-lap-registers ((mask index))
    (let ((field wrapper-cache-no))
      (flatten-lap
        (opcode :move (operand :cvar 'mask) mask)
        (opcode :move (operand :cvar 'field) field)
        (opcode :move (emit-wrapper-ref wrapper field) wrapper-cache-no)
        (opcode :move (operand :ilogand wrapper-cache-no mask) primary)))))

(defun emit-n-wrapper-compute-primary-cache-location (wrappers primary miss-label)
  (with-lap-registers ((field index)
               (mask index))
    (let ((add-wrapper-cache-numbers
       (flatten-lap
        (gathering1 (flattening-lap)
           (iterate ((wrapper (list-elements wrappers))
             (i (interval :from 1)))
         (gather1
          (with-lap-registers ((wrapper-cache-no index))
            (flatten-lap
             (opcode :move (emit-wrapper-ref wrapper field) wrapper-cache-no)
             (opcode :izerop wrapper-cache-no miss-label)
             (opcode :move (operand :i+ primary wrapper-cache-no) primary)
             (when (zerop (mod i wrapper-cache-number-adds-ok))
               (opcode :move (operand :ilogand primary mask) primary))))))))))
      (flatten-lap
       (opcode :move (operand :constant 0) primary)
       (opcode :move (operand :cvar 'field) field)
       (opcode :move (operand :cvar 'mask) mask)
       add-wrapper-cache-numbers
       (opcode :move (operand :ilogand primary mask) primary)
       (opcode :move (operand :i1+ primary) primary)))))



;;;
;;;  NIL              means nothing so far, no actual arg info has NILs
;;;                   in the metatype
;;;  CLASS            seen all sorts of metaclasses
;;;                   (specifically, more than one of the next 4 values)
;;;  T                means everything so far is the class T
;;;  STANDARD-CLASS   seen only standard classes
;;;  BUILT-IN-CLASS   seen only built in classes
;;;  STRUCTURE-CLASS  seen only structure classes
;;;
(defun raise-metatype (metatype new-specializer)
  (let ((standard  (find-class 'standard-class))
    (fsc       (find-class 'funcallable-standard-class))
;    (structure (find-class 'structure-class))
    (built-in  (find-class 'built-in-class)))
    (flet ((specializer->metatype (x)
         (let ((meta-specializer
             (if (and (eq *boot-state* 'complete)
                  (eql-specializer-p x))
             (class-of (class-of (eql-specializer-object x)))
             (class-of x))))
           (cond ((eq x *the-class-t*) t)
             ((*subtypep meta-specializer standard)  'standard-instance)
             ((*subtypep meta-specializer fsc)       'standard-instance)
;                    ((*subtypep meta-specializer structure) 'structure-instance)
             ((*subtypep meta-specializer built-in)  'built-in-instance)
             (t (error "PCL can not handle the specializer ~S (meta-specializer ~S)."
                   new-specializer meta-specializer))))))
      ;;
      ;; We implement the following table.  The notation is
      ;; that X and Y are distinct meta specializer names.
      ;;
      ;;   NIL    <anything>    ===>  <anything>
      ;;    X      X            ===>      X
      ;;    X      Y            ===>    CLASS
      ;;
      (let ((new-metatype (specializer->metatype new-specializer)))
    (cond ((null metatype) new-metatype)
          ((eq metatype new-metatype) new-metatype)
          (t 'class))))))


(defun emit-fetch-wrapper (metatype argument dest miss-label &optional slot)
  (let ((exit-emit-fetch-wrapper (make-symbol "exit-emit-fetch-wrapper")))
    (with-lap-registers ((arg t))
      (ecase metatype
    (standard-instance
      (let ((get-std-inst-wrapper (make-symbol "get-std-inst-wrapper"))
        (get-fsc-inst-wrapper (make-symbol "get-fsc-inst-wrapper")))
        (flatten-lap
          (opcode :move (operand :arg argument) arg)
          (opcode :std-instance-p arg get-std-inst-wrapper)       ;is it a std wrapper?
          (opcode :fsc-instance-p arg get-fsc-inst-wrapper)       ;is it a fsc wrapper?
          (opcode :go miss-label)
          (opcode :label get-fsc-inst-wrapper)
          (opcode :move (operand :fsc-wrapper arg) dest)       ;get fsc wrapper
          (and slot
           (opcode :move (operand :fsc-slots arg) slot))
          (opcode :go exit-emit-fetch-wrapper)
          (opcode :label get-std-inst-wrapper)
          (opcode :move (operand :std-wrapper arg) dest)       ;get std wrapper
          (and slot
           (opcode :move (operand :std-slots arg) slot))
          (opcode :label exit-emit-fetch-wrapper))))

    (class
      (when slot (error "Can't do a slot reg for this metatype."))
      (let ((get-std-inst-wrapper (make-symbol "get-std-inst-wrapper"))
        (get-fsc-inst-wrapper (make-symbol "get-fsc-inst-wrapper"))
        (get-built-in-wrapper (make-symbol "get-built-in-wrapper")))
        (flatten-lap
          (opcode :move (operand :arg argument) arg)
          (opcode :std-instance-p arg get-std-inst-wrapper)
          (opcode :fsc-instance-p arg get-fsc-inst-wrapper)
          (opcode :built-in-instance-p arg get-built-in-wrapper)
          ;; If the code falls through the checks above, there is a serious problem
          (opcode :label get-fsc-inst-wrapper)
          (opcode :move (operand :fsc-wrapper arg) dest)
          (opcode :go exit-emit-fetch-wrapper)
          (opcode :label get-built-in-wrapper)
          (opcode :move (operand :built-in-wrapper arg) dest)
          (opcode :go exit-emit-fetch-wrapper)
          (opcode :label get-std-inst-wrapper)
          (opcode :move (operand :std-wrapper arg) dest)
          (opcode :label exit-emit-fetch-wrapper))))
    (structure-instance
      (when slot (error "Can't do a slot reg for this metatype."))
      (error "Not yet implemented"))
    (built-in-instance
      (when slot (error "Can't do a slot reg for this metatype."))
      (let ((get-built-in-wrapper (make-symbol "get-built-in-wrapper")))
        (flatten-lap
          (opcode :move (operand :arg argument) arg)
          (opcode :built-in-instance-p arg get-built-in-wrapper)
          (opcode :go miss-label)
          (opcode :label get-built-in-wrapper)
          (opcode :move (operand :built-in-wrapper arg) dest))))))))


;;;
;;; Some support stuff for getting a hold of symbols that we need when
;;; building the discriminator codes.  Its ok for these to be interned
;;; symbols because we don't capture any user code in the scope in which
;;; these symbols are bound.
;;;

(defvar *dfun-arg-symbols* '(.ARG0. .ARG1. .ARG2. .ARG3.))

(defun dfun-arg-symbol (arg-number)
  (or (nth arg-number (the list *dfun-arg-symbols*))
      (intern (format nil ".ARG~A." arg-number) *the-pcl-package*)))

(defvar *slot-vector-symbols* '(.SLOTS0. .SLOTS1. .SLOTS2. .SLOTS3.))

(defun slot-vector-symbol (arg-number)
  (or (nth arg-number (the list *slot-vector-symbols*))
      (intern (format nil ".SLOTS~A." arg-number) *the-pcl-package*)))

(defun make-dfun-lambda-list (metatypes applyp)
  (gathering1 (collecting)
    (iterate ((i (interval :from 0))
          (s (list-elements metatypes)))
      (progn s)
      (gather1 (dfun-arg-symbol i)))
    (when applyp
      (gather1 '&rest)
      (gather1 '.dfun-rest-arg.))))

(defun make-dlap-lambda-list (metatypes applyp)
  (gathering1 (collecting)
    (iterate ((i (interval :from 0))
          (s (list-elements metatypes)))
      (progn s)
      (gather1 (dfun-arg-symbol i)))
    (when applyp
      (gather1 '&rest))))

(defun make-dfun-call (metatypes applyp fn-variable)
  (let ((required
      (gathering1 (collecting)
        (iterate ((i (interval :from 0))
              (s (list-elements metatypes)))
          (progn s)
          (gather1 (dfun-arg-symbol i))))))
    (if applyp
    `(apply   ,fn-variable ,@required .dfun-rest-arg.)
    `(funcall ,fn-variable ,@required))))


;;;
;;; Here is where we actually fill, recache and expand caches.
;;;
;;; The function FILL-CACHE is the ONLY external entrypoint into this code.
;;; It returns 4 values:
;;;   a wrapper field number
;;;   a cache
;;;   a mask
;;;   an absolute cache size (the size of the actual vector)
;;;
;;;
(defun fill-cache (field cache nkeys valuep limit-fn wrappers value)
  (declare (values field cache mask size))
  (fill-cache-internal field cache nkeys valuep limit-fn wrappers value))

(defun default-limit-fn (nlines)
  (case nlines
    ((1 2 4) 1)
    ((8 16)  4)
    (otherwise 6)))


;;;
;;; Its too bad Common Lisp compilers freak out when you have a defun with
;;; a lot of LABELS in it.  If I could do that I could make this code much
;;; easier to read and work with.
;;;
;;; Ahh Scheme...
;;;
;;; In the absence of that, the following little macro makes the code that
;;; follows a little bit more reasonable.  I would like to add that having
;;; to practically write my own compiler in order to get just this simple
;;; thing is something of a drag.
;;;
(eval-when (compile load eval)

(proclaim '(special *nkeys* *valuep* *limit-fn*))

(defvar *local-cache-functions*
    `((cache     () .cache.)
      (nkeys     () *nkeys*)
      (valuep    () *valuep*)
      (limit-fn  () *limit-fn*)
      (line-size () .line-size.)
      (mask      () .mask.)
      (size      () .size.)
      (nlines    () .nlines.)
      ;;
      ;; Return T IFF this cache location is reserved.  The only time
      ;; this is true is for line number 0 of an nkeys=1 cache.
      ;;
      (line-reserved-p (line)
        (and (= (nkeys) 1)
         (= line 0)))
      ;;
      ;; Given a line number, return the cache location.  This is the
      ;; value that is the second argument to cache-ref.  Basically,
      ;; this deals with the offset of nkeys>1 caches and multiplies
      ;; by line size.  This returns nil if the line is reserved.
      ;;
      (line-location (line)
        (and (null (line-reserved-p line))
         (if (= (nkeys) 1)
             (* line (line-size))
             (1+ (* line (line-size))))))
      ;;
      ;; Given a cache location, return the line.  This is the inverse
      ;; of LINE-LOCATION.
      ;;
      (location-line (location)
        (if (= (nkeys) 1)
        (/ location (line-size))
        (/ (1- location) (line-size))))
      ;;
      ;; Given a line number, return the wrappers stored at that line.
      ;; As usual, if nkeys=1, this returns a single value.  Only when
      ;; nkeys>1 does it return a list.  An error is signalled if the
      ;; line is reserved.
      ;;
      (line-wrappers (line)
        (when (line-reserved-p line) (error "Line is reserved."))
        (let ((location (line-location line)))
          (if (= (nkeys) 1)
          (cache-ref (cache) location)
          (gathering1 (collecting)
            (dotimes (i (nkeys))
              (gather1 (cache-ref (cache) (+ location i))))))))
      ;;
      ;; Given a line number, return the value stored at that line.
      ;; If valuep is NIL, this returns NIL.  As with line-wrappers,
      ;; an error is signalled if the line is reserved.
      ;;
      (line-value (line)
        (when (line-reserved-p line) (error "Line is reserved."))
        (and (valuep)
         (cache-ref (cache) (+ (line-location line) (nkeys)))))
      ;;
      ;; Given a line number, return true IFF that line has data in
      ;; it.  The state of the wrappers stored in the line is not
      ;; checked.  An error is signalled if line is reserved.
      (line-full-p (line)
        (when (line-reserved-p line) (error "Line is reserved."))
        (not (null (cache-ref (cache) (line-location line)))))
      ;;
      ;; Given a line number, return true IFF the line is full and
      ;; there are no invalid wrappers in the line, and the line's
      ;; wrappers are different from wrappers.
      ;; An error is signalled if the line is reserved.
      ;;
      (line-valid-p (line wrappers)
        (when (line-reserved-p line) (error "Line is reserved."))
        (let ((loc (line-location line))
          (wrappers-mismatch-p (null wrappers)))
          (dotimes (i (nkeys) wrappers-mismatch-p)
        (let ((wrapper (cache-ref (cache) (+ loc i))))
          (when (or (null wrapper)
                (invalid-wrapper-p wrapper))
            (return nil))
          (unless (and wrappers
                   (eq wrapper
                   (if (consp wrappers) (pop wrappers) wrappers)))
            (setq wrappers-mismatch-p t))))))
      ;;
      ;; How many unreserved lines separate line-1 and line-2.
      ;;
      (line-separation (line-1 line-2)
        (let ((diff (- line-2 line-1)))
          (cond ((zerop diff) diff)
            ((plusp diff) diff)
            (t
             (if (line-reserved-p 0)
             (1- (+ (- (nlines) line-1) line-2))
             (+ (- (nlines) line-1) line-2))))))
      ;;
      ;; Given a cache line, get the next cache line.  This will not
      ;; return a reserved line.
      ;;
      (next-line (line)
        (if (= line (1- (nlines)))
        (if (line-reserved-p 0) 1 0)
        (1+ line)))
      ;;
      ;; Given a line which has a valid entry in it, this will return
      ;; the primary cache line of the wrappers in that line.  We just
      ;; call COMPUTE-PRIMARY-CACHE-LOCATION-FROM-LOCATION, this is an
      ;; easier packaging up of the call to it.
      ;;
      (line-primary (field line)
        (location-line
          (compute-primary-cache-location-from-location
        field (cache) (line-location line) (mask) (nkeys))))
      ;;
      ;;
      (fill-line (line wrappers value)
        (when (line-reserved-p line)
          (error "Attempt to fill a reserved line."))
        (let ((loc (line-location line)))
          (cond ((= (nkeys) 1)
             (setf (cache-ref (cache) loc) wrappers)
             (when (valuep) (setf (cache-ref (cache) (1+ loc)) value)))
            (t
             (iterate ((i (interval :from 0))
                   (w (list-elements wrappers)))
               (setf (cache-ref (cache) (+ loc i)) w))
             (when (valuep) (setf (cache-ref (cache) (+ loc (nkeys))) value))))))
      ;;
      ;; Blindly copy the contents of one cache line to another.  The
      ;; contents of the <to> line are overwritten, so whatever was in
      ;; there should already have been moved out.
      ;;
      ;; For convenience in debugging, this also clears out the from
      ;; location after it has been copied.
      ;;
      (copy-line (from to)
        (if (line-reserved-p to)
        (error "Copying something into a reserved cache line.")
        (let ((from-loc (line-location from))
              (to-loc (line-location to)))
          (modify-cache (cache)
            (dotimes (i (line-size))
              (setf (cache-ref (cache) (+ to-loc i))
                (cache-ref (cache) (+ from-loc i)))
              (setf (cache-ref (cache) (+ from-loc i))
                nil))))))
      ;;
      ;;
      ;;
      (transfer-line (from-cache from-line to-cache to-line)
        (if (line-reserved-p to-line)
        (error "transfering something into a reserved cache line.")
        (let ((from-loc (line-location from-line))
              (to-loc (line-location to-line)))
          (modify-cache to-cache
            (dotimes (i (line-size))
              (setf (cache-ref to-cache (+ to-loc i))
                (cache-ref from-cache (+ from-loc i))))))))
      ))

(defmacro with-local-cache-functions ((cache) &body body &environment env)
  `(let ((.cache. ,cache))
     (declare (type simple-vector .cache.))
     (multiple-value-bind (.mask. .size. .line-size. .nlines.)
     (compute-cache-parameters *nkeys* *valuep* .cache.)
       (declare (type fixnum .mask. .size. .line-size. .nlines.))
       (progn .mask. .size. .line-size. .nlines.)
       (labels ,(mapcar #'(lambda (fn) (assq fn *local-cache-functions*))
            (pickup-local-cache-functions body env))
     ,@body))))

(defun pickup-local-cache-functions (body env)
  (let ((functions ())
    (possible-functions (mapcar #'car *local-cache-functions*)))
    (labels ((walk-function (form context env)
           (declare (ignore env))
           (when (and (eq context :eval)
              (consp form)
              (symbolp (car form)))
         (let ((name (car form)))
           (when (and (not (memq name functions))
                  (memq name possible-functions))
             (pushnew name functions)
             (walk (cddr (assq name *local-cache-functions*))))))
           form)
         (walk (body)
           (walk-form `(progn . ,body) env #'walk-function)))
      (walk body)
      functions)))

)


;;;
;;; returns 4 values, <field> <cache> <mask> <size>
;;; It tries to re-adjust the cache every time it makes a new fill.  The
;;; intuition here is that we want uniformity in the number of probes needed to
;;; find an entry.  Furthermore, adjusting has the nice property of throwing out
;;; any entries that are invalid.
;;;
(defun fill-cache-internal (field cache nkeys valuep limit-fn wrappers value)
  (let ((*nkeys* nkeys)
    (*valuep* valuep)
    (*limit-fn* limit-fn))
    (with-local-cache-functions (cache)
      (flet ((4-values-please (f c)
           (multiple-value-bind (mask size)
           (compute-cache-parameters *nkeys* *valuep* c)
         (values f c mask size))))
    (let ((easy-fill-p (fill-cache-p nil field cache wrappers value)))
      (if easy-fill-p
          (4-values-please field cache)
          (multiple-value-bind (adj-field adj-cache)
          (adjust-cache field cache wrappers value)
        (if adj-field
            (4-values-please adj-field adj-cache)
            (multiple-value-bind (exp-field exp-cache)
            (expand-cache field cache wrappers value)
              (4-values-please exp-field exp-cache))))))))))

;;;
;;; returns T or NIL
;;;
(defun fill-cache-p (forcep field cache wrappers value)
  (with-local-cache-functions (cache)
    (let* ((primary (location-line (compute-primary-cache-location field (mask) wrappers))))
      (multiple-value-bind (free emptyp)
      (find-free-cache-line primary field cache wrappers)
    (when (or forcep emptyp) (fill-line free wrappers value) t)))))

(defun fill-cache-from-cache-p (forcep field cache from-cache from-line)
  (with-local-cache-functions (from-cache)
    (let ((primary (line-primary field from-line)))
      (multiple-value-bind (free emptyp)
      (find-free-cache-line primary field cache)
    (when (or forcep emptyp)
      (transfer-line from-cache from-line cache free)
      t)))))

(defun entry-in-cache-p (field cache wrappers value)
  (declare (ignore field value))
  (with-local-cache-functions (cache)
    (dotimes (i (nlines))
      (unless (line-reserved-p i)
    (when (equal (line-wrappers i) wrappers) (return t))))))

;;;
;;; Returns NIL or (values <field> <cache>)
;;;
;;; This is only called when it isn't possible to put the entry in the cache
;;; the easy way.  That is, this function assumes that FILL-CACHE-P has been
;;; called as returned NIL.
;;;
;;; If this returns NIL, it means that it wasn't possible to find a wrapper
;;; field for which all of the entries could be put in the cache (within the
;;; limit).
;;;
(defun adjust-cache (field cache wrappers value)
  (with-local-cache-functions (cache)
    (let ((ncache (get-cache (size))))
      (do ((nfield field (next-wrapper-field nfield)))
      ((null nfield) (free-cache ncache) nil)
    (labels ((try-one-fill-from-line (line)
           (fill-cache-from-cache-p nil nfield ncache cache line))
         (try-one-fill (wrappers value)
           (fill-cache-p nil nfield ncache wrappers value)))
      (if (and (dotimes (i (nlines) t)
             (when (and (null (line-reserved-p i))
                (line-valid-p i wrappers))
               (unless (try-one-fill-from-line i) (return nil))))
           (try-one-fill wrappers value))
          (return (values nfield ncache))
          (flush-cache-internal ncache)))))))


;;;
;;; returns: (values <field> <cache>)
;;;
(defun expand-cache (field cache wrappers value)
  (declare (values field cache) (ignore field))
  (with-local-cache-functions (cache)
    (multiple-value-bind (ignore size)
    (compute-cache-parameters (nkeys) (valuep) (* (nlines) 2))
      (let* ((ncache (get-cache size))
         (nfield (wrapper-field 'number)))
    (labels ((do-one-fill-from-line (line)
           (unless (fill-cache-from-cache-p nil nfield ncache cache line)
             (do-one-fill (line-wrappers line) (line-value line))))
         (do-one-fill (wrappers value)
           (multiple-value-bind (adj-field adj-cache)
               (adjust-cache nfield ncache wrappers value)
             (if adj-field
             (setq nfield adj-field ncache adj-cache)
             (fill-cache-p t nfield ncache wrappers value))))
         (try-one-fill (wrappers value)
           (fill-cache-p nil nfield ncache wrappers value)))
      (dotimes (i (nlines))
        (when (and (null (line-reserved-p i))
               (line-valid-p i wrappers))
          (do-one-fill-from-line i)))
      (unless (try-one-fill wrappers value)
        (do-one-fill wrappers value))
      (values nfield ncache))))))


;;;
;;; This is the heart of the cache filling mechanism.  It implements the decisions
;;; about where entries are placed.
;;;
;;; Find a line in the cache at which a new entry can be inserted.
;;;
;;;   <line>
;;;   <empty?>           is <line> in fact empty?
;;;
(defun find-free-cache-line (primary field cache &optional wrappers)
  (declare (values line empty?))
  (with-local-cache-functions (cache)
    (let ((limit (funcall (limit-fn) (nlines)))
      (wrappedp nil))
      (when (line-reserved-p primary) (setq primary (next-line primary)))
      (labels (;;
           ;; Try to find a free line starting at <start>.  <primary>
           ;; is the primary line of the entry we are finding a free
           ;; line for, it is used to compute the seperations.
           ;;
           (find-free (p s)
         (do* ((line s (next-line line))
               (nsep (line-separation p s) (1+ nsep)))
              (())
           (if (null (line-valid-p line wrappers)) ;If this line is empty or
               (return (values line t))               ;invalid, just use it.

               (let ((osep (line-separation (line-primary field line) line)))
             (if (and wrappedp (>= line primary))
                 ;;
                 ;; have gone all the way around the cache, time to quit
                 ;;
                 (return (values line nil))

                 (when (cond ((or (= nsep limit)) t)
                     ((= nsep osep) (zerop (random 2)))
                     ((> nsep osep) t)
                     (t nil))
                   ;;
                   ;; Try to displace what is in this line so that we
                   ;; can use the line.
                   ;;
                   (return (values line (displace line)))))))

           (if (= line (1- (nlines))) (setq wrappedp t))))
           ;;
           ;; Given a line, attempt to free up that line by moving its
           ;; contents elsewhere. Returns nil when it wasn't possible to
           ;; move the contents of the line without dumping something on
           ;; the floor.
           ;;
           (displace (line)
         (if (= line (1- (nlines))) (setq wrappedp t))
         (multiple-value-bind (dline dempty?)
             (find-free (line-primary field line) (next-line line))
           (when dempty? (copy-line line dline) t))))

    (find-free primary primary)))))